The importance of end-capping or terminating polycarbonates with certain end or terminal groups is well known. Polycarbonates which are not so end-capped are generally insufficiently heat stable since the free phenolic end groups provide reactive sites which are generally detrimental to the thermal stability of the polycarbonate. Well known and conventionally used end-capping agents include phenol compounds such as p-tertiary-butyl phenol, chroman-I, and phenol itself.
The prior art also discloses other types of compounds that are effective end-capping agents for the carbonate polymers. These end-capping agents include the alkylphenols disclosed in U.S. Pat. No. 4,269,964 and Japanese Patent Publication No. 34992/76; the alkanol amines disclosed in U.S. Pat. No. 3,085,992; the imides disclosed in U.S. Pat. No. 3,399,172; aniline and methyl aniline as disclosed in U.S. Pat. No. 3,275,601; and the primary and secondary amines disclosed in U.S. Pat. No. 4,001, 184. Some other end-capping agents described in the prior art include the aromatic amines disclosed in U.S. Pat. No. 3,028,365; and the ammonium compounds, ammonia, primary cycloalkyl amines, and primary aliphatic or aralkyl amines disclosed in U.S. Pat. No. 4,111,910.
However, according to Schnell, Chemistry and Physics of Polycarbonates (1964), page 138, ammonium hydroxide and amines saponify polycarbonates back to the monomers. This is supported by Bolgiano in U.S. Pat. No. 3,223,678 wherein it is disclosed that small amounts of amines such as monoethanolamine and morpholine break or degrade polycarbonates into lower molecular weight polycarbonates. Thus, this area of chemistry is generally not completely understood and is one where the empirical approach is still generally the method used to determine whether a particular compound or class of compounds will function as an effective end-capping agent for polycarbonates. This area is still further complicated by the fact that even though a particular compound may be an effective chain-terminating agent for polycarbonates, its presence in the polymer chain may adversely affect some of the advantageous physical properties of polycarbonates.